US20070076157A1

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Info

Publication number: US20070076157A1
Application number: US11/242,069
Authority: US
Inventors: Wen-Chun Wang; Ming-Chang Yu; Henta Kang
Original assignee: Wintek Corp
Current assignee: Wintek Corp
Priority date: 2005-10-04
Filing date: 2005-10-04
Publication date: 2007-04-05

Abstract

A structure of liquid crystal display (LCD) with a wide viewing angle is presented. In this invention, a slit pattern of a pixel electrode is definded by using an etching process. Thereafter, a reflection layer which defines a reflective region and a transmissive region is constructed along the top or bottom of the slit of the pixel electrode, and wherein a slit or bump pattern can be included in the top electrode further. Therefore, by adjusting the relative positions of the slit or bump structures in the electrodes and by using the fringe effect of electric field, the tilt direction of the LC molecules in a LC cell is controlled and the effect of semi-transmitted wide viewing angle of multi-domain division is formed.

Description

FILED OF THE INVENTION

The invention presents a kind of structure of LCD (liquid crystal display) with a wide viewing angle. The point is that the technology of wide viewing angle with multi-domain division and build-in refective function is constructed.

BACKGROUND OF THE INVENTION

An impediment to the use of conventional LCD is the limited viewing angle problem, which allows for a good vision with viewing angles of 45 degree from center left to right. However, for the development of faceplates with larger dimensions and wider applications and for the strict requirement of visional reception, it is important for a LCD with a wide viewing angle.

There are two technologies for a wide viewing angle.

One is an external adhesive mode and the other is a build-in mode (e.g., Multi-domain Vertical Alignment (MVA), In Plane Switchin (IPS)). The American patent U.S. Pat. No. 6,380,996 “Optical compensatory sheet and liquid crystal display” uses a transparent compensatory film with a dual index of refraction (□n<0) to compesate the phase delay from the TN LC cell, so that the purpose of wide viewing angle is achieved, as shown inFIG. 1. Although the external adhesive mode can promot the viewing angle with precision diffusers, the diffusers are fixed and can't compensate any gray-scale and any angle. So, the natual gray-scale transformation in TN LCD still exists.

U.S. Pat. No. 6,661,488 “Vertically-aligned (VA) liquid crystal display device” proposed a kind of protrusion-like bump to produce a pretilt angle by the LC itself, as shown inFIG. 2. When the vertex angle of the bump becomes larger, the tilt angle of the long axis of a molecule becomes smaller.

FIG. 3 shows a kind of LCD with a dual domain MVA mode. When the voltage is off, the long axis of LC molecule is perpendicular to the screen and only the molecule close to the bump electrode is tilt a little, so that the light can not pass through the top and the bottom polarizers. When the voltage is on, the molecules close to the bump electrode, together with other molecules, are twisted and perpendicular to the surface of the bump immediately, i.e. the long axes of molecules are tilt to the screen. Therefore, the transmittance is going up to realize the light adjustment. Since the adjacent LC molecules in the dual-domain mode are symmetric and the long axes point to different directions, the compensation of light can be achieved in the MVA mode.

The practical vision effect is medium gray-scale in the view looking B and is high gray-scale or low gray-scale in the view looking A and C, as shown inFIG. 4. However, before the compensation of light, the viewing angle can be modified only in the up, down, left and right directions by MVA mode, and the other directions are not ideal. Even looking at the screen with very large viewing angle in the special orientation, the transformation of gray-scale occurs. The strength of electric fields is not uniform due to the special arrangment of the electrodes, and which can make the gray-scale display incorrect. It is necessary to increase the drive voltage up to 13.5V to control the rotation of LC molecules precisively, so a lot of power is wasted.

U.S. Pat. No. 5,598,285 ┌Liquid crystal display device┘ is an IPS mode, wherein the strip-like electrodes are placed parallel to the substrate, as shown inFIG. 5. When the voltage is applied to the electrodes, the LC molecules initially arranged along the horizontal electrode reorient themselves in the direction perpendicular to the electrode, and the long axes of the LC molecules are still paralleled to the substrate. The LC molecules can rotate to the specified angles by contolling the voltages, and the polarizers can adjust the transmittance of the polarized light, so that different color scales can display. The LC molecules are not twist-nematic type, but their long axes are paralleled to the substrate.

Since the electrodes of the IPS mode are on the same side of the substrae but not on both sides as other LC modes, the in-plane electric field is constructed to drive LC molecules with lateral motions. When the voltage is applied to the electrode, the LC molecules nearby the electrode get much power to twist 90 degree immediately. However, the LC molecules far from the electrode can not get the same power, so the motion is slow. Only increasing the drive voltage, the LC molecules far from the electrodecan can get enough power. Therefore, the drive voltage for the IPS mode is high, and typically is about 15 volt. Besides, the IPS mode needs more backlight lamps, because the in-plane electrode will reduce the ratio of the slit and the transmittance.

The semi-transmissive LCD involves the merits of the transmissive LCD and the reflective LCD. In order to have the semi-transmissive effect, the American patent U.S. Pat. No. 6,195,140 ┌Liquid crystal display in which at least one pixel includes both a transmissive region and reflective region┘ proposed a kind of technique with dual cell gap. The cell gap of the transmissive region and reflective region in the pixel is divided into different gap heights. When d_R=d_T/2, the transmissive region and reflective region have the same difference of optical path, as shown inFIG. 6.

In addition, a kind of transmissive and reflective LCD is applied to the LC device with single cell gap, which is added a micro reflective film on the surface of the bottom plate, as shown inFIG. 7. The micro reflective film allows light to pass through the bottom. When light incidents from the top, the light will reflect by the micro reflective film. However, the efficiency of usage can't achieve the predicted result.

SUMMARY OF THE INVENTION

Therefore, in order to solve the above problems, the main purpose of this invention is to control the different tilt directions of the LC molecules by using the fringe effect of electric field in vertical direction, so that the vertical alignment of multi-domain division is formed and the transmissive region and reflective region in the pixel electrode are defined, thereby the wide viewing angle LCD with reflective effect is constructed.

Another purpose of the invention is to form a wide viewing angle LCD with reflective effect of the structure of the semi-transmissive LCD. Since the LCD has the merits of the reflective and transmissive LCDs, the definition and power saving can be achieved at indoor and outdoor conditions.

In this invention, a pixel electrode is established on the first substrate, and a slit pattern of the pixel electrode is definded by using an etching process. A reflection layer that defines the reflective and transmissive regions formed along the top or bottom of the slit of the pixel electrode, and the reflective layer is covered with a polarizing layer. A top electrode and a polarizer are established on the second substrate. The polarization axis of the polarizer is orthogonal to the polarizing layer, and the top electrode includes a slit or bump pattern structure. Therefore, by adjusting the relative positions of the slit or bump structures of the electrodes and by using the fringe effect of the electric field, the tilt direction of the molecule in the LC cell is controlled and the alignment of multi-domain division is constructed. At the same time, a semi-transmissive LCD with both reflective and transmissive regions is formed, so that good definition and power saving can be achieved at indoor and outdoor conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the schematic diagram of a compensatory film with an external adhesive mode.

FIG. 2 shows the schematic diagram of a LCD with a build-in MVA mode.

FIG. 3 shows the schematic diagram of a LCD with a build-in MVA mode.

FIG. 4 shows the schematic diagram of real visional effect of a LC with a build-in MVA mode.

FIG. 5 shows the schematic diagram of a LCD with a build-in IPS mode.

FIG. 6 shows the schematic diagram of a dual cell gap LCD.

FIG. 7 shows the schematic diagram of a single cell gap LCD.

FIG. 8 shows the first schematic diagram of the LCD structure in the invention.

FIG. 9 shows the top-view schematic diagram of the LCD pixel in the invention.

FIGS. 10A to10G show the top-view schematic diagrams of the slits of the pixel electrode and top electrode.

FIGS. 11A to11G show the schematic diagrams of the relative positions of the slits.

FIG. 12 shows the schematic diagram of the invention without applied voltages.

FIG. 13 shows the schematic diagram of the invention with applied voltages.

FIG. 14 shows the second schematic diagram of the LCD structure in the invention.

FIG. 15 shows the third schematic diagram of the LCD structure in the invention.

FIG. 16 shows the fourth schematic diagram of the LCD structure in the invention.

FIG. 17 shows the fifth schematic diagram of the LCD structure in the invention.

FIG. 18 shows the sixth schematic diagram of the LCD structure in the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detail contents and illustrations of the technologies of the invention are given below.

FIG. 8 shows the first schematic diagram of the LCD structure of the invention. The structure contains thefirst substrate10 with a TFT (thin firm transistor) on the surface. Apixel electrode11 is estabished on the first substrate, and aslit pattern110 of thepixel electrode11 is definded by using an etching process. Areflection layer12 that defines the reflective region R and transmissive region T is deposited partially on thepixel electrode11 along the boundary of theslit110. Thereflection layer12 is a metal material (e.g., Al, Ag, Cr, AlNd and so on) with low resistivity and high reflection character. Thereflection layer12 and thepixel electrode11 are covered with apolarizing layer13, and finally theplarizing layer13 is covered with thefirst alignment film14.

Thesecond substrate20 with a color filter has atop electrode21, and apolarizer23 is on the outside surface of thesecond substrae20. The polarization axis of thepolarizer23 is orthogonal to thepolarizing layer13. Thetop electrode21 has aslit structure21a, and theslit structure21acontains at least one point-like slit. Thetop electrode21 and theslit structure21aare covered with thesecond alignment film24, and theslit structure21aand theslit structure110 of thepixel electrode11 are separated in the vertival direction, i.e. theslit structure21aof thetop electrode21 and theslit structure110 of thepixel electrode11 do not overlap each other.FIG. 9 shows that the

slit structures

110 and21aare formed in the center of the pixel electrode. Finally, theLC cells30 are established between thefirst substrate10 and thesecond substrae20.

There are two portions of the statement of the invention. In wide viewing angle, by adjusting the relative positions between theslit structure110 of thepixel electrode11 on thefirst substrate10 and theslit structure21aof thepixel electrode21 on thesecond substrate20, theslit structure21aand theslit structure110 are separated in the vertival direction. The patterns of the

slit structures

110 and21acan be the combination of the cross shape, herringbone shape, ] shape, [ shape, < shape, X shape, S shape, petal shape, horizontal configuration shape, or vertical slot shape, as shown fromFIGS. 10A to10G and fromFIGS. 11A to11F. By adjusting the relative positions between the

slits

110 and21aand by using the fringe effect of electric field of the two slit structures to control the tilt direction of the LC molecules in theLC cell30, the effect of semi-transmissive wide viewing angle with multi-domain division is formed.

In reflective function, the outside light is reflected by thereflection layer12 around theslit structure110 of thepixel electrode11. When the light passes through thepolarizer23, theLC cell30 and thepolarizing layer13, the reflective region R and the transmissive region T have the same polarzation state to achieve the effect of semi-transmission and semi-reflection.

AsFIG. 12 indicates, when the driving voltage is not applied to the LC, the arrangement of the long axes of the LC molecules in theLC cell30 is perpendicular to thesecond substrate20 and thefirst substrate10. When the backlight passes through thepolarizing layer13 and theLC cells30 and arrives at thesecond substrate20, the polarization direction of the polarized light is perpendicular to the polarization axis of theporlarizer23 on thesecond substrate20, so that the light is cut off to produce a dark frame. Similarly, the arrangement of the long axes of the LC molecules in theLC cell30 is perpendicular to thesecond substrate20 and thefirst substrate10 in the reflective region. When the outside light passes through thepolarizer23 on the surface of thesecond substrate20 and through theLC cells30, the polarization direction of the polarized light is perpendicular to the polarization axis of theporlarizing layer13 on thefirst substrate10, so that the incident light is absorbed to produce a dark frame.

AsFIG. 13 indicates, when the drive voltage is applied to the LC, in the transmissive region, the molecules of theLC cells30 are tilted down around thepixel electrode11 and thetop electrode21 due to the electric field of the fringes in vertical direction. The arrangement of the long axes of LC molecules is perpendicular to the direction of the applied voltage. When the backlight passes through thepolarizing layer13 and theLC cells30, the polarization direction of the polarized light is not perpendicular to the polarization axis of theporlarizer23 on thesecond substrate20, so that the light passes through to produce a bright frame.

As for in the reflective region R, the molecules of theLC cells30 are tilted down around thepixel electrode11 and thetop electrode21 due to the electric field of the fringes in vertical direction, and the arrangement of the long axes of LC molecules is perpendicular to the direction of the applied voltage. When the outside light passes through thepolarizer23 on the surface of thesecond substrate20 and through theLC cells30, the polarization direction of the polarized light is not perpendicular to the polarization axis of theporlarizing layer13 on thefirst substrate10. The outside light is reflected by thereflection layer12 and passes through theLC cells30, and the polarized direction of the reflection light is not perpendicular to the polarized direction of thepolarizer23 on thesecond substrate20. The reflection light passes to produce a bright frame.

FIG. 14 shows the second schematic diagram of the LCD structure of the invention. AsFIG. 14 indicates, thetop electrode21 on thesecond substrate20 includes at least one point-like bump211, which is different from theFIG. 8, and thetop electrode21 and thebump211 are covered with analignment film24. Thebump211 and theslit structure110 of thepixel electrode11 are separated in the vertival direction, i.e. both do not overlap each other. The patterns of theslit structure110 and thebump211 can be asFIGS. 10A to10G and FIGS.11 to11F.

Another construction is that thetop electrode21 is a flate plane covered with analignment film24, as shown inFIG. 15. Finally, theLC cells30 are established between thefirst substrate10 and thesecond substrate20.

FIG. 16 shows the fourth schematic diagram of the LCD structure of the invention. AsFIG. 16 indicates, the construction has thefirst substrate100, and the pattern of thereflection layer120 is formed on the substrate by an etching process to define the reflective region R and the transmissive region T. Thereflection layer120 is a metal material (e.g., Al, Ag, Cr, AlNd and so on) with low resistivity and high reflection character. Besides, thefirst substrate100 contains TFTs, and thereflection layer120 and thefirst substrate100 are covered with thepolarizing layer130, wherein at least one open window is formed to expose thereflection layer120. Then, thepixel electrode110 is constructed on thepolarizing layer130, and theelectrode110 forms theslit structure110aby an etching process, and theelectrode110 covers thereflection layer120. Theslit structure110ais established around the pattern of thereflection layer120. Finally, theelectrode110 is covered with thealignment film140.

Thesecond substrate200 contains a color filter and is established with atop electrode210. The outside surface of thesubstrate200 contains apolarizer230. The direction of the polarization axis of thepolarizer230 is orthogonal to thepolarizing layer130. Thetop electrode210 includes at least one point-like bump210a, and thetop electrode210 and thebump210aare covered with analignment film240. Theslit structure210aof thetop electrode210 and theslit structure110aof thepixel electrode110 are separated in the vertival direction, as shown inFIG. 9,FIGS. 10A to10G andFIGS. 11A to11F. The

slit structures

110aand210aare fabricated on the center of the pixel electrode. Finally, theLC cells30 are established between thefirst substrate100 and thesecond substrate200.

The principles of the wide viewing angle and the reflective function, as mentioned above, are summarized: to use the arrangement of theslit structure110aof thepixel electrode110 and theslit structure210aof thetop electrode210 and to form the effect of multi-domain semi-transmissive wide viewing angle by adjusting the relative positions of the

slit structures

110aand210aand by using the fringe effect of electric field of the

slit structures

110aand210ato control the tilt directions of theLC molecules300. Besides, by using the reflective region made of thereflection layer120 under thepixel electrode110, when the light passes through thepolarizer230 and theLC cell300, the reflective region R and the transmissive region T have the same polarized direction to achieve the semi-transmissive and semi-reflective effect.

FIG. 17 shows the fifth schematic diagram of the LCD structure of the invention. AsFIG. 17 indicates, thetop electrode210 on thesecond substrate200 includes at least one point-like bump211a, which is different from theFIG. 16, and thetop electrode210 and thebump211aare covered with thealignment film240. Thebump211aand theslit structure110aof thepixel electrode110 are separated in the vertival direction. The patterns of theslit structure110aand thebump211acan be asFIGS. 10A to10G andFIGS. 11A to11F.

Another construction is that thetop electrode210 on thesecond substrate200 is a flate plane covered with analignment film240, as shown inFIG. 18. Finally, theLC cells300 are established between thefirst substrate100 and thesecond substrate200.

To sum up, the invention is based on the function of the wide viewing angle to define the transmissive region and the reflective region at the pixel electrode, thereby the wide viewing angle LCD with reflective effect is formed. By using the fringe effect of electric field in the vertical direction, the different tilt directions of the LC molecules are controlled, and the LCD with reflective function and vertical alignment of multi-domain division is constructed. Compared with the previous tecknologies, the invention has the merits that the slits form the wide viewing angle and the light in the transmissive and reflective regions is used totally.

While the above mentions are some better examples for demonstration, but not the limitation of application in this invention. All the homogeneous modification and variations of the invention are included in what is claimed in this invention.

Claims

1. A structure of LCD (liquid crystal display) with a wide viewing angle, comprising:

a first substrate, wherein a pixel electrode is established on the first substrate, and the pixel electrode has slit structures;

a reflection layer which is established around the slit structures of the pixel electrode and covers a part of the pixel electrode;

a polarizing layer which covers the reflection layer and the pixel electrode;

a first alignment film which covers the polarizing layer;

a second substrate, wherein an electrode is established on a surface of the second substrate faced to the first substrate;

a second alignment film which covers a top electrode; and

a LC cell which is established between the first alignment film and the second alignment film.

2. The structure of LCD with a wide viewing angle ofclaim 1, wherein the first substrate includes at least one TFT.

3. The structure of LCD with a wide viewing angle ofclaim 1, wherein the polarizer is established on the surface of the second substrate and the direction of a polarization axis of the polarizer is orthogonal to the polarizing layer.

4. The structure of LCD with a wide viewing angle ofclaim 1, wherein the second substrate further includes one color filter.

5. The structure of LCD with a wide viewing angle ofclaim 1, wherein a slit structure of the pixel electrode includes at least one point-like slit.

6. The structure of LCD with a wide viewing angle ofclaim 1, wherein the reflection layer is a metal material with low resistivity and high reflection character.

7. The structure of LCD with a wide viewing angle ofclaim 1, wherein the slit structure of the top electrode and the slit structure of the pixel electrode are separated in the vertival direction.

8. The structure of LCD with a wide viewing angle ofclaim 7, wherein the slit structure of the top electrode includes at least one point-like slit.

9. The structure of LCD with a wide viewing angle ofclaim 1, wherein the top electrode includes at least one bump structure and the bump structure and the slit structure of the pixel electrode are separated in the vertival direction.

10. The structure of LCD with a wide viewing angle ofclaim 9, wherein the bump structure of the top electrode includes at least one point-like bump.

11. A kind of structure of LCD (liquid crystal display) with a wide viewing angle, comprising:

a first substrate, wherein a pattern of a reflection layer is established on the first substrate;

a polarizing layer which covers the reflection layer and the first substrate;

a pixel electrode which is established on the surface of the polarizer layer and covers a reflective region and further has slits around the pattern of the reflection layer;

a first alignment film which covers the pixel electrode;

a second substrate, wherein a top electrode is established on the surface of the second substrate faced to the first substrate;

a second alignment film which covers the top electrode; and

12. The structure of LCD with a wide viewing angle ofclaim 11, wherein the polarizer is established on the surface of the second substrate and the direction of a polarization axis of the polarizer is orthogonal to the polarizing layer.

13. The structure of LCD with a wide viewing angle ofclaim 11, wherein the first substrate includes at least one TFT.

14. The structure of LCD with a wide viewing angle ofclaim 11, wherein the second substrate further includes one color filter.

15. The structure of LCD with a wide viewing angle ofclaim 11, wherein a slit structure of the pixel electrode includes at least one point-like slit.

16. The structure of LCD with a wide viewing angle ofclaim 11, wherein the reflection layer is a metal material with low resistivity and high reflection character.

17. The structure of LCD with a wide viewing angle ofclaim 11, wherein the top electrode includes at least one slit structure, and the slit structure and the slit structure of the pixel electrode are separated in the vertival direction.

18. The structure of LCD with a wide viewing angle ofclaim 17, wherein the slit structure of the top electrode includes at least one point-like slit.

19. The structure of LCD with a wide viewing angle ofclaim 11, wherein the top electrode includes at least one bump structure and the bump structure and the slit structure of the pixel electrode are separated in the vertival direction.

20. The structure of LCD with a wide viewing angle ofclaim 19, wherein the bump structure of the top electrode includes at least one point-like bump.